1. Field of the Invention
The present invention relates to the preparation of para-acyloxybenzene sulfonates, and, more especially, to the preparation of para-acyloxybenzene sulfonates by acid catalysis, and wherein the acyloxy moiety of such sulfonates contains from 7 to 12 carbon atoms.
2. Description of the Prior Art
It is known to this art, from French Pat. No. 2,164,619, Example 1, to prepare the title compounds from an aliphatic acid chloride and potassium phenol sulfonate by direct condensation in an anhydrous reaction medium. The speed of condensation between the acid chloride and the phenol sulfonate is extremely slow (20 hours at 150.degree. C.) and the product formed is very difficult to isolate. A large amount of HCl also forms in the process and is not always easy to eliminate.
It is also known [see Pueschel, Tenside, 7 (5), pp. 249-54 (1970)] to prepare these compounds by a method which differs slightly from that of French Pat. No. 2,164,619, but in the presence of an acid acceptor to avoid the elimination of gaseous hydrochloric acid. The product formed is neutralized by sodium carbonate, but as a result it is very difficult to separate the product obtained from the sodium chloride formed during neutralization.
The slowness of the reaction in which the acid chloride is condensed with the phenol sulfonate has prompted those skilled in this art to raise the reaction temperature considerably, but strongly colored products are then formed. Since such products are in fact principally used in detergency, however, it is necessary to produce perfectly white materials in order to meet commercial requirements.
It too is known, from French Pat. No. 2,299,321, to prepare para-acyloxybenzene sulfonates by condensing a powdered phenol sulfonate with acetic anhydride in vapor state; the reaction can be carried out dry, for acetic anhydride has a boiling point of 140.degree. C., but it is not possible to proceed in this fashion as a means for condensing, e.g., nonanoic anhydride, with phenol sulfonate, since nonanoic anhydride has a boiling point of 260.degree. C.
Nonetheless, it was hitherto unknown to condense an acid anhydride with a phenol sulfonate in a liquid reaction medium.